1. Field of the Invention
The invention concerns disposable garments such as diapers for infants and for incontinent adults, more specifically a pressure-sensitive adhesive closure that can be peeled open and reclosed. The invention particularly concerns improvements in the closure.
2. Description of the Related Art
Many disposable diapers have a reinforced fastening area (sometimes called a "target area") to which a pressure-sensitive adhesive fastening tape (sometimes called a "closure tab") is pressed and adhered to fasten the diaper around an infant or other person wearing the diaper. Whether or not the fastening area is reinforced, the fastening tape should remain securely in place while the diaper is being worn and should be cleanly peelable from the fastening area and capable of being securely reattached. Although forces which may cause the fastening tape to become loose during use of the diaper generally occur at low speeds, e.g., up to about 30 cm/min., a person who readjusts or removes a diaper may judge the closure to be of poor quality if the fastening tape peels off too easily or in an excessively shocky manner when removed quickly, e.g., at about 500 to 1250 cm/min. We are not aware of any report in the prior art of a pressure-sensitive adhesive closure for a diaper that would provide high peel resistance both at low and high speeds without being excessively shocky at high speeds, nor do we believe that any such diaper closure has been sold or offered for sale.
U.S. Pat. No. 4,376,147 (Byrne et al.) concerns an embossed thermoplastic polyolefin film which has a matte finish that "is extremely low in gloss even on both sides and tape adhesion values are achieved which render the film particularly useful for fabrication into . . . disposable diapers where such adhesion values are needed" (col. 2, lines 54-59). The adhesive which provides "such adhesion values" is not disclosed, and the only adhesion values given are at col. 5, line 38 without indicating their significance.
U.S. Pat. No. 4,546,029 (Cancio et al.), like the Byrne patent, concerns an embossed thermoplastic polyolefin film simulating a matte or dull finish, but its embossing is asymmetric as opposed to the symmetry of the Byrne embossing, thus providing "a totally different visual appearance" (col. 3, lines 9-10). Unlike the Byrne patent, the Cancio patent explains the reported tape adhesion values. Its Table (col. 7) gives such values for the asymmetrically embossed film, showing improvement versus the Byrne film, but as in the Byrne patent, there is no disclosure of the adhesive tape used in making those measurements.
U.S. Pat. No. 4,436,520 (Lipko et al.) says that the exposed surface of a film used as a diaper back sheet typically is embossed to reduce gloss, but that "the embossing materially reduces the adhesion of the embossed surface for the closure tabs so that the diaper is no longer secure in its use on the infant" (col. 1, lines 19-22). The Lipko patent concerns the discovery "in embossed films of polyethylene having a (45.degree.) gloss of no greater than 8, the adhesion of the embossed surface is markedly enhanced when said surface has a mean value of maximum profile height of less than 150 and maximum peak to valley height of less than 230" (col. 1, lines 35-40). The profile measurements are made with a "Surtronic" 3 apparatus sold by Taylor-Hobson. The adhesive tape used for making the reported tape adhesion values is not disclosed.
U.S. Pat. No. 4,237,889 (Gobran) concerns an improved closure tab or fastening tape for a disposable diaper. The improvement is in the tape backing which is a substantially untensilized crystalline polypropylene or linear polyethylene foil having one smooth face and one textured face. There is no disclosure of a pressure-sensitive adhesive to be used on the fastening tape.
European Patent Application 82110676.4 (Raphael et al.), published Aug. 6, 1983, concerns a diaper having an impermeable outer sheet which has been calendered to provide a matte appearance. This is reinforced at the fastening area with an impermeable sheet which may be polypropylene that is perfectly smooth as opposed to the matte surface of the underlying sheet. The smoothness is said to improve adhesion by the fastening tape.
German Patent Application P 33 38 201.8 (Widlund), laid open Apr. 26, 1984, indicates that a disposable diaper typically has an outer polyethylene layer to which a pressure-sensitive adhesive fastening tape will not adhere well because the surface of the polyethylene layer is not sufficiently smooth. This problem is avoided by applying to the fastening area of the diaper one or several plastic strips which are selected to provide good adhesion by the fastening tape and preferably are smooth and flat.